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Homework Help: Intensity of the incident light

  1. Apr 5, 2009 #1
    1. The problem statement, all variables and given/known data

    Unpolarized light is incident on a system of three polarizers. The second polarizer is oriented at an angle of 33.0° with respect to the first and the third is oriented at an angle of 45.0° with respect to the first. If the light that emerges from the system has an intensity of 2.3 W/m2, what is the intensity of the incident light?

    2. Relevant equations


    3. The attempt at a solution

    I know that after I0 passes through the first polarizer, it is 1/2I0. After it passes through the second, I thought it would be 1/2I0cos2(33), and after it passes through the third, 1/2I0cos2(33)cos2(45).
    This would all equal 2.3, which I was given.
    So I set up my final equation as:
    1/2I0cos2(33)cos2(45) = 2.3, or
    I0= 2.3 / (1/2cos2(33)cos2(45).

    I solved and got 13.08, but that is incorrect. Can anyone offer any insight? Thanks.
  2. jcsd
  3. Apr 6, 2009 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    For the third polarizer, use the angle between it and the second polarizer.

    45° is the angle between the third and first polarizer.
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